When an eyeglass frame is of the rimless type, the shaping of each of the corrective lenses intended to be joined to the frame is followed by drilling each lens appropriately so as to enable the temples and the nose bridge of the rimless frame to be fastened thereon. The drilling may be performed with an edger or with a separate drilling machine by means of a drill bit.
Most often, the following drilling method is implemented. First, the future wearer chooses the desired frame provided with presentation lenses. The optician then places the presentation lenses one after the other into a device for determining the positions of the drill holes. Each presentation lens is pre-drilled in its temporal and nasal portions and thus serves as a model for appropriately shaping and drilling the target corrective lens that is to be joined to the frame chosen by the future wearer.
The presentation lens is thus placed in a support between lighting means for producing a projected view and image capture means, with the front face of the lens facing towards the lighting means. A plate made out of frosted glass allows a projected image of the shadow of the lens to be formed on the capture means.
The image of the shadow of the presentation lens is acquired. Thus an overall image of the drill hole is obtained that presents a geometrical shape that is complex. This overall image is displayed on a screen. A virtual identification-marking ring is provided that the operator can view and move around the screen so as to superpose the ring onto the overall image of the drill hole of the presentation lens, while also sizing and centering the ring. The operator validates the positioning and the sizing, and the processor system stores the position of the center and the transverse dimension (i.e. its diameter if the hole is round) of the identification-marking ring as being the position of the center and the transverse dimension of the drill hole to be drilled in the corrective lens.
After the corrective lens has been shaped to match the outline of the presentation lens, a drill bit having an appropriate diameter is brought to face the corrective lens at the stored position for the hole to be drilled. The corrective lens is thus drilled by means of the drill bit being free to move relative to the lens along the axis of rotation of the drill bit. If the diameter of the drill bit is less than the desired diameter, the resulting hole is widened by imparting an appropriate transverse movement to the drill bit.
However, in particular for lenses that are greatly curved, it is observed that an often significant error exists between the position of the drill hole drilled in the corrective lens and the real position and dimension of the drill hole in the presentation lens. This error in the positioning and the dimension of the hole leads to difficulties in mounting the lens onto the temples and the nose bridge and may even, in some circumstances, end up with mounting being impossible or of poor quality, or may even oblige the optician to perform a reworking operation that is time consuming and that requires expert knowledge. Further, the corrective lens may, as a result, be poorly positioned in front of the eye of the wearer, thereby degrading its performance in optical correction.